What is missing is that it is normal to get low amps with the lower voltage because battery "acceptance" is higher in amps at any SOC if its voltage is higher.
When I get more internet access, I will post one of my ugly graphs showing the comparison charging profile of the PM3-100 where it drops to 13.7 as soon as battery reaches 14.6 with its modified profile where it just stays at 14.6 after battery voltage reaches that.
Meanwhile text only version is that it starts with four 6s at 50% SOC and in both cases runs steady at 100a till battery SOC is 72% and it hits 14.6v ( the SOC you hit 14.6 varies with charging rate--higher rate, lower SOC for that--ie the 75amper will hit 14.6 at a higher SOC about 78% other things being equal) In both cases amps start to taper from the SOC it hits that 14.6.
OK, so now lets compare at 80% SOC and at 84% SOC, where first number is mod staying at 14.6 and second number is with unmod at 13.7
80%SOC 65a/25a
84%SOC 40a/12a
Time taken to reach 84% from 72% was 1 hr mod vs 2 hrs unmod.
You can figure roughly where the OP was for SOC on his four batts from the amps he saw as described since by then it made no difference he had a 75amper vs a 100 amper. At that SOC where amps are lower than 75 it would be about the same profile on four batts.
